I just bought "Sir, you are being hunted", it is a very unique game. You try to survive by avoiding robots and eating food. You can also find weapons, cook food, search for loot, etc. It has a very nice game design and it is like an exploration game FPS. The only objective is to look for parts and then you can do whatever you want.
You go across five islands looking for parts, either blasting your way through, or being stealthy and setting traps and hiding. It is rather unforgiving though because you can only save at a few locations and you die easily. I'm not sure if it's worth $20 right now since it's still in development but why not give it a go.